The non-chemical physical property profile of a composition can dramatically alter the in-process handling and performance, and possibly the in vitro or in vivo performance, of a particular material. In other words, a given chemical composition having a first physical property profile might be suitable for inhalation; whereas, the same chemical composition having a different second physical property profile might be unsuitable for inhalation. Likewise, a particular excipient having a first physical property profile might be better suitable for tabletting by compression than would be the same excipient having a different second physical property profile.
For example, the suitability of different physical forms of a material used as a carrier for dry powder inhalation will vary according to the non-chemical physical property profile of the various physical forms of the material. The delivery of a drug by inhalation allows for deposition of the drug in different sections of the respiratory tract, e.g., throat, trachea, bronchi and alveoli. Generally, the smaller the particle size, the longer the particle will remain suspended in air and the farther down the respiratory tract the drug can be delivered. Drugs are delivered by inhalation using a nebulizer, metered dose inhaler (MDI), or dry powder inhaler (DPI).
Dry powder inhalers provide powder pharmaceuticals in aerosol form to patients. In order to generate an aerosol, the powder in its static state must be fluidized and entrained into the patient's inspiratory airflow. The powder is subject to numerous cohesive and adhesive forces that must be overcome if it is to be dispersed. Fluidization and entrainment requires the input of energy to the static powder bed. The particle size, shape, surface morphology and chemical composition of carrier particles can influence aerosol dispersion. Increased drug dispersion and deposition is generally observed with smaller carrier size and increased proportion of fine particles. Elongated carriers generally increased aerosol dispersibility and drug FPF (fine particle fraction), possibly due to increased duration in the airstream drag forces. Carriers with smooth surfaces produced higher respirable fractions. Low respirable fractions were obtained from carriers with macroscopic surface roughness or smooth surfaces, whereas high respirable fractions were obtained from carriers with microscopic surface roughness, where smaller contact area and reduced drug adhesion occurred at the tiny surface protrusions. Thus for dry powder inhaler formulations, the size of carrier particles should be selected on the basis of a balance between these interrelated performance characteristics. Specifically, inter-particulate forces should be such that the drug particles adhere to the carrier (to aid in blending, uniformity, and allow the entrainment of drug into the inspiratory air-stream), yet also allow detachment of the fine drug particles from the surface of the coarser carrier particles so that delivery to the lung can be facilitated. In view of the above, different physical forms of the known solid carrier lactose may or may not be suitable for dry powder inhalation.
The same general impact of physical form upon excipient behavior is true for other pharmaceutical processes used to make dosage forms such as a tablet, liquid, suspension, emulsion, film, laminate, pellet, powder, bead, granule, suppository, ointment, cream, etc. In other words, a single excipient will need to be made in different physical forms in order for it to be better suited for particular uses. For improved tabletting by compression, for example, an excipient will preferably have improved flow. Good flow characteristics are desirable in order to facilitate handling and processing in a tablet press or capsule-filling machine. It will also have a compressibility within a particular range depending upon the role of the excipient in the tablet. If an excipient is going to be used in a constitutable liquid formulation, the excipient will preferably not clump when placed in the liquid and it will dissolve completely and quickly. Even though many of these are highly desired features in a solid excipient, it is very difficult to obtain any single excipient having all of these features. For this reason, among others, many different grades of excipients are developed in the pharmaceutical industry.
Drying methods such as tray drying, freeze drying, spray drying, fluidized bed spray granulation, and fluidized bed spray agglomeration, among others, are used in the pharmaceutical industry to prepare solids from feed solutions, emulsions, suspensions or slurries. The physical properties of the isolated solid will depend upon the properties of the feed material and the parameters employed in and the equipment used for the drying method employed.
Spray drying entails atomizing a solids-containing feed solution or suspension to form atomized droplets directed into a stream of hot gas in a drying chamber thereby evaporating the liquid carrier from the droplets resulting in the formation of spherical particles. Fluidized bed spray drying is a modified form of spray drying wherein a spray drying process is performed in the presence of a fluidized bed (fluidized by the stream of hot gas) of fine particles such that the atomized droplets collide with and adhere to the fluidized particles. By modifying the solids content of the feed solution and in the drying chamber, a spray drying apparatus can be made to agglomerate or granulate the solids in a process called fluidized bed spray agglomeration or fluidized bed spray granulation, respectively. Moreover, the use of a rectangular versus cylindrical spray drying apparatus will have an impact upon the physical properties of the resulting product.
In an exemplary fluidized bed spray agglomeration/granulation with a cylindrical apparatus, powder feed enters the solids feed inlet at a controllable speed, and the liquid spray system sprays liquid feed from the top or bottom of the fluidized bed into the material. Heated fluidizing gas flows upward from the inlet through the bottom screen, fluidizing the powder feed or seed particles in the fluidized-bed chamber. Simultaneously, classifying gas flows upward through the discharge pipe at a velocity that's controlled to blow fine particles back into the fluidized bed, allowing only larger particles with a falling velocity higher than the discharge pipe's classifying air velocity to discharge through the pipe. This allows control of the product's particle size while keeping the product dust-free. Dust removed from the exhaust air by the circular unit's external deducting equipment can be recirculated to the recycle inlet for further processing. During this process, the smaller particles fuse with each other or with larger particles to form agglomerates. As a result, the particle size distribution of the particles in the fluidized bed increases such that the percentage of fine particles present in the product is reduced as compared to the fluidized feed material.
Solubilization of poorly water soluble compounds in aqueous media is often very difficult. Therefore, artisans have employed solubilization enhancers, such as cyclodextrins, in the aqueous medium. Parent (underivatized)cyclodextrins and their derivatives are well known excipients that contain 6, 7, or 8 glucopyranose units and are referred to as α-, β-, and γ-cyclodextrin, respectively. Each cyclodextrin subunit has secondary hydroxyl groups at the 2 and 3 positions and a primary hydroxyl group at the 6-position. The cyclodextrins may be pictured as hollow truncated cones with hydrophilic exterior surfaces and hydrophobic interior cavities.
β-CD has been reportedly prepared in a variety of different forms using different finishing processes. American Maize Products (French patent No. 2,597,485) recommends freeze-drying and spraying as suitable methods for recovering cyclodextrin ethers from aqueous solutions. However, the powders obtained according to these various techniques have poor dissolution. In addition, these powders do not flow easily and possess mediocre compression properties.
U.S. Pat. No. 6,555,139 to Sharma discloses a method for microfluidizing β-CD in combination with a hydrophobic drug to yield a smooth, latex-like microsuspension.
U.S. Pat. No. 5,674,854 to Bodley et al. discloses a composition containing an inclusion complex of β-CD and diclofenac. The composition can be prepared by spray agglomeration.
U.S. Patent Application Publication No. 20040234479 to Schleifenbaum discloses a flavor or fragrance containing a cyclodextrin particle containing the cyclodextrin particle and a flavor or fragrance, wherein the cyclodextrin particle has a particle size in a range of 50 to 1000μ. The cyclodextrin particle comprises a cellulose ether and cyclodextrin, wherein the cyclodextrin particle is obtained by a single stage fluidized bed process from a spray mixture, and wherein a gas introduction temperature is from 80° to 180° C. and a gas outlet temperature is from 40° to 95° C.
European Patent Application No. EP 392 608 describes a method for producing powdered cyclodextrin complexes wherein the particle size is less than 12μ, preferably less than 5μ. Suitable processes for doing so include spray-drying and freeze-drying. The '608 application states that small particle sizes of CD often exhibit reduced pourability or flowability and may dust easily. For this reason, the art suggests the use of cyclodextrin complex particles having particle sizes of at least 50μ.
U.S. Patent Application Publication No. 20030065167 to Lis et al. discloses a process for preparing a directly compressible β-CD. The process includes “a step of dehydrating hydrated beta-cyclodextrin to a water content of less than 6%, preferably less than 4% and more preferably still less than or equal to 2% by weight, followed by forced rehydration to a water content greater than 10%, preferably greater than 12% and more preferably still greater than or equal to 13% by weight.
The impact of the drying step or finishing step in the preparation of hydroxypropyl-β-cyclodextrin (HP-β-CD) obtained from a syrup containing the same has been explored. U.S. Patent Application Publication No. 20030028014 to Sikorski et al. discloses an agglomerated HP-β-CD and a process from making the same. The agglomerated product is made in a double drum dryer. It reportedly has low dusting and good dissolution in water. The particle size of the product is about 30 to 200μ.
U.S. Pat. No. 5,756,484 to Fuertes et al. discloses a pulverulent HP-β-CD composition and a method for its preparation. The HP-β-CD has a centered particle size free of fine particles and an appreciably improved capacity to dissolve in aqueous medium. The HP-β-CD is made by spraying a solution of HP-β-CD on a moving pulverulent bed of HP-β-CD particles.
The physical and chemical properties of the parent cyclodextrins can be modified by derivatizing the hydroxyl groups with other functional groups. One such derivative is a sulfoalkyl ether cyclodextrin.

Sulfoalkyl ether cyclodextrin (SAE-CD) derivatives are well known as are their uses in a wide range of applications. SAE-CD derivatives are particularly useful in solubilizing and/or stabilizing drugs. A sulfobutyl ether derivative of beta cyclodextrin (SBE-β-CD), in particular the derivative with an average of about 7 substituents per cyclodextrin molecule (SBE7-β-CD), has been commercialized by CyDex, Inc. as CAPTISOL®. The anionic sulfobutyl ether substituent dramatically improves the aqueous solubility of the parent cyclodextrin. In addition, the presence of the charges decreases the ability of the molecule to complex with cholesterol as compared to the hydroxypropyl derivative. Reversible, non-covalent, complexation of drugs with CAPTISOL® cyclodextrin generally allows for increased solubility and stability of drugs in aqueous solutions.
CAPTISOL®, prepared by spray drying, is used in the commercial formulations VFEND® and GEODON®. It has become a leading cyclodextrin derivative for use in pharmaceutical formulations and thus is important to the industry.
Methods of preparing SAE-CD derivatives are varied but generally include the general steps of sulfoalkylation followed by isolation. The chemical property profile of the SAE-CD is established during the sulfoalkylation step. For example, altering reaction conditions during sulfoalkylation can vary the average degree of substitution for and the average regiochemical distribution of sulfoalkyl groups in the SAE-CD. The alkyl chain length of the sulfoalkyl functional group is determined according the sulfoalkylating agent used. And use of a particular alkalizing agent during alkylation would result in formation of a particular SAE-CD salt, unless an ion exchange step were performed subsequent to sulfoalkylation.
In general, known processes for the sulfoalkylation step include, for example 1) exposure of underivatized parent cyclodextrin under alkaline conditions to an alkylating agent, e.g. alkyl sultone or a haloalkylsulfonate; 2) optional addition of further alkalizing agent to the reaction milieu to consume excess alkylating agent; and 3) neutralization of the reaction medium with acidifying agent. The vast majority of literature processes conduct the sulfoalkylation step in aqueous media; however, some references disclose the use of pyridine, dioxane, or DMSO as the reaction solvent for sulfoalkylation. Literature discloses the use of an alkalizing agent in order to accelerate the sulfoalkylation reaction. Upon completion of the sulfoalkylation step, isolation and purification of the SAE-CD is conducted.
Several different isolation processes for SAE-CD following sulfoalkylation and neutralization are described. In general, an aqueous liquid containing SAE-CD is dried to remove water to form a solid. The literature suggests various methods for removal of water from an aqueous solution containing SAE-CD. Such methods include conventional freeze-drying, spray drying, oven drying, vacuum oven drying, roto-evaporation under reduced pressure, vacuum drying or vacuum drum drying. See, for example, Ma (S.T.P. Pharma. Sciences (1999), 9(3), 261-266), CAPTISOL® (sulfobutyl ether beta-cyclodextrin sodium; Pharmaceutical Excipients 2004; Eds. R. C. Rowe, P. J. Sheskey, S. C. Owen; Pharmaceutical Press and American Pharmaceutical Association, 2004) and other references regarding the preparation of SAE-CD derivatives.
The art, therefore, is lacking teaching on the methods of preparing and using SAE-CD derivatives having particular non-chemical physical property profiles. Given the importance of SAE-CD to the pharmaceutical industry, it would be a significant improvement in the art to provide SAE-CD derivatives having particular non-chemical physical property profiles so that such forms can be tailored for particular purposes.